Permanent magnet system for the bundled guidance of an electron beam over a relatively long path, especially for traveling wave tubes



P. MEYERER 3,329,915 PERMANENT MAGNET SYSTEM FOR THE BUNDLED GUIDANCE OF AN ELECTRON July 4. 1967 BEAM OVER A RELATIVELY LONG PATH, ESPECIALLY FOR TRAVELING WAVE TUBES a Sheets-Sheet 1 Filed Aug. 6, 1965 INVENTOR Pau/ Maya/er ATTYS,

July 4. 1967 P. MEYERER 3,329,915

PERMANENT MAGNET SYSTEM FOR THE BUNDLED GUIDANCE OF AN ELECTRON BEAM OVER A RBLATIVELY LONG PATH, ESPECIALLY FOR TRAVELING WAVE TUBES Filed Aug. 6, 1965 5 Sheets-Sheet 2 NSSNNSSNNS-SNN NSSNNSS'NNSSNNS Fig.5

I '7 l L -13 I N s s N' N s s N N s s N s NSSN INVENTOR Paa/ fieyer'er' BY .rdvzfuz SNNSS 'r- ATTYS,

July 4. 1967 p. MEYERER 3,329,915

PERMANENT MAGNET SYSTEM FOR THE BUNDLED GUIDANCE OF AN ELECTRON BEAM OVER A RELATIVELY LONG PATH, ESPECIALLY FOR TRAVELING WAVE TUBES Filed Aug. 6, 1965 5 Sheets-Sheet 3 Fig.6

INV E N TOR Pau/ Maya/er ATTYS.

United States Patent O Claims. cl. 335-210) This invention relates to a permanent magnet system for the bundled guidance of an electron beam over a relatively long path, especially for traveling tubes, in which the permanent magnets are arranged axially symmetrically to the electron path, and pole pieces, which are arranged in succession in electron beam direction and are permeated by the electron beam, alternately magnetically connect oppositely disposed like poles of the permanent magnets in such a way that along the electron path there arises a magnetic field, alternating in direction, with approximately a sine-shaped course of the magnetic field strength.

Permanent magnet systems of this type are already known, and, indeed, in various forms of construction. In one of such forms the magnet system consists of short permanent magnet rings which are arranged one behind the other coaxially with respect to the electron path with like poles being adjacent, and disposed between like poles there are provided annular disk-like pole pieces which have hollow cylindrical projections in the vicinity of the electron path. Another known permanent magnet system for the generation of a magnetic field with approximately sine-shaped field strength distribution consists of permanent magnets which form a quadrilateral in planes perpendicular to the electron path. There, like poles of the permanent magnets, magnetized in peripheral direction of the quadrilateral are adjacent to one another. These poles are alternately connected with the oppositely disposed like poles by perpendicularly extending pole pieces.

Animportant problem which arises in the focusing of electron beams by means of magnetic fields is, as is Well known, the avoidance of transverse magnetic interference components. In the known periodic permanent magnet systems mentioned it has heretofore been endeavored to keep the magnetic transverse fields small by making the pole pieces of a highly permeable soft iron which are constructed, as to their dimension and their spatial allocation to one another, with extreme precision. It has here proved, however, that the pole pieces must not exceed manufacturing tolerances on the order of 0.01 mm., whereby, of course, a great expenditure in the production of the pole pieces is required.

In order to reduce the manufacturing technical expenditure in pole pieces for a periodic permanent magnet system, it has already been proposed that the pole pieces be prefabricated as rectangular sheet metal strips, provided in the middle with a bore and subsequently twisted twice, which can be accomplished by a forging process. In this connection it also has been suggested that there be inserted into the bore of the pole piece a soft iron ring to compensate disturbances in the rotational symmetry of the periodic magnetic field, which may be evoked through a deviation of the twisted surfaces of the pole pieces from a precisely perpendicular position to one another.

The invention has as its problem, with simple means to create a permanent magnetic system which generates a practically completely rotationally symmetrical magnetic field, alternating in direction. For the solution of this problem, in a permanent magnet system of the type here- 7 3,329,915 Patented July 4, 1967 tofore mentioned it is proposed according to the invention that the electron path be enclosed, at least at intervals, by a tube which, in a manner in itself known, is constructed of alternately soft magnetic and nonmagnetic rings. In this system the soft magnetic rings of an odd ordinal number border directly on the pole piece and are symmetrically surrounded thereby, while the soft magnetic rings of an even ordinal number are arranged, in each case, as seen in electron beam direction, between adjacent pole pieces.

In a permanent magnet system for the generation of a homogeneous magnetic field along the discharge path of a transit time tube, it is already a known practice, for the elimination of interfering magnetic transverse components, to array highly permeable, thin disks one upon another, which are separated by nonmagnetic spacing rings and surround the electron path. There, in distinction to the present invention, there are arranged between the magnet poles of a system a large number of highly permeable disks, so that it is not possible to distinguish between disks of an even and of an odd ordinal number. The arrangement cannot be compared with the invention, however, for the additional reason that in the known system all the soft magnetic disks have to be very thin to avoid presenting a considerable magnetic shunt, which would require a considerable enlargement of the permanent magnets.

The important advance of the invention resides in the feature that with a device that is very simple, from the viewpoint of mechanics and maunfacturing technology, faults in the rotational symmetry of a periodic magnetic field, which are due to the unavoidable manufacturing tolerances of the magnet systems known for the generation of such fields, are compensated. There the soft magnetic rings of an odd ordinal number (pole piece rings) eliminate dissymmetries of the magnetic guide field which occur in their immediate area by reason of manufacturing inaccuracies of the pole pieces. The soft magnetic rings of even ordinal number (homogenization rings) than compensate transverse fields that are caused by faults in the spatial arrangements of the pole pieces and by imperfections on the end faces of the pole pieces. In this manner it is possible to use forged pole pieces instead of the ground soft-iron pole pieces heretofore common, in which practice it is additionally possible to achieve an appreciable improvement in the rotational symmetry of the field.

The invention is of special importance for a perodic magnet system in which the permanent magnets are arranged in the form of a closed quadrangle and alternately oppositely disposed, are poled corners of the quadrangle like joined with one another by soft iron pole pieces. Such a periodic magnetic system has, per se, the advantage that without great stray fields a simple adaptation is achievable to the requirement of the magnetic flux and the magnetic potential for the exact focusing of the electron beam. In consequence of the interdigital type arrangement of the soft iron pole pieces, however, there exists the danger that the field will have an ellipticicity, which, in an arrangement according to the invention is effectively eliminated by the action of the homogenization rings.

In the drawings, 'wherein like reference numerals indicate like or corresponding parts:

FIG. 1 is an end elevational view of a permanent magnet focusing system embodying the invention;

FIG. 2 is a sectional view taken approximately on the line AA of FIG. 1;

FIG. 3 is a sectional view, similar to FIG. 2, of a megnetic focusing device of modified construction;

'FIG. 4 is a sectional view similar to FIG. 3, illustrating a modification of the structure therein disclosed;

3 FIG. is a sectional view taken approximately on the line C-D of FIG. 4; and

FIG. 6 is a view, similar to FIG. 2 ilustrating additional details of the tube structure.

Referring to FIGS. 1 and 2, magnets 1, 2, 3 and 4 are arranged, in known manner, axially symmetrical to the axis of the electron beam in such a way that the magnets form the sides of a square. The magnets are magnetized in peripheral direction of the square and like poles are disposed at respective corners of the square. The opposite corners of like polarity are alternately connected with one another in horizontal and vertical direction by ole pieces. The pole pieces 5 have in each case a central bore 6 for the reception of the discharge vessel of an electron tube, into which is inserted according to the invention a tube 7 which is built up alternately of soft magnetic and nonmagnetic rings. The soft magnetic rings (pole piece rings) 8 of an odd ordinal number are so arranged in the bores 6 of the pole pieces 5 that such rings border directly on the pole pieces 5 and are symmetrically surrounded thereby. There will be distinguished from the pole piece rings 8, the soft magnetic rings (homogenization rings) 9 of an even ordinal number which are, in each case, centered between two adjacent pole piece rings 8 and are separated therefrom by the nonmagnetic spacing rings 10. The individual rings 8, 9 and 10 are advantageously joined with one another by soldering or cementing and processing in common into the finished tube 7.

As illustrated, the homogenization rings 2 have, expediently in axial direction, a smaller dimension than the pole piece rings 8, so that the rings 9 exert as little influence as possible on the magnetic field course in electron beam direction. The homogenization rings 9, even if they are very narrow, however, effect a balancing out of rotational asymmetries of the magnetic field which may be caused by the face ends of the pole pieces 5. Moreover, through the homogenization rings 9 it is assured that no ellipticity of the magnetic field will occur which in itself is caused -by the interdigitally arranged soft-iron pole pieces 5. In the prior known magnet systems of the type of FIGS. 1 and 2 attempts have been made to avoid the ellipticity of the magnetic field by the method that the ratio of the pole piece width a to the inside diameter d of tube 7 was greater than two. This ratio can now be made smaller, whereby a higher magnetic induction is achieved along the axis of the magnetic system. The pole piece rings 8 elimina-te disturbances in the rotational symmetry of the magnetic field which are due directly to faults in the construction of the pole pieces 5.

FIGURE 3 illustrates a magnetic focusing device for the generation of a magnetic field, alternating periodically in direction, in which, in known manner, annular permanent magnets 11 are so arranged successively that like poles are disposed adjacent one another and between such like poles there are provided annular disk-shaped pole pieces 12. Disposed within the focusing device there is again a tube 7 which coaxially encloses the electron path. The tube 7 is, as in the construction of FIGS. 1 and 2, alternately built up of pole piece rings 8, nonmagnetic spacing rings 10 and soft magnetic homogenization rings 9, in which system the spacing rings 10 have dimensions on the same order of magnitude as the homogenization rings 9. The pole piece rings 8 are so dimensioned that, in a manner known per se, they appear as hollow cylindrical projection or extensions on the pole pieces 12.

In a focusing device according to FIG. 3 the pole piece rings and the pole pieces expediently can be made in one piece. FIG. 4 illustrates a cross section and FIG. 5 a section along the line C-D of FIG. 4 of a corresponding permanent magnet system. The permanent magnets 11 are, in this case, divided into two half-shelfs 11 and 11, so that they can be subsequently inserted between the projections 13 which are present on the pole piece rings 8 and correspond to the pole pieces 12, in FIG. 3.

In a permanent magnet system according to the invention, advantageously the tube, which is built up alternately of the soft magnetic pole pieces, homogenization rings and the nonmagnetic spacing rings, can simultaneously comprise the vacuum envelope of a traveling wave tube or be mounted upon the vacuum envelope of the tube. This feature is of particular importance in a permanent magnet system which, as previously known, can be swung open in two mirror-symmetrical halves, whereby, with favorable dimensioning of the magnet system, is capable of receiving a traveling wave tube, both ends of which are thicker than the central portion of the tube, containing the delay line. It has been proved that in such a hingeable permanent magnet system, by reason of the division of the system into two halves, inadmissibly high magnetic transverse fields cannot, without difiiculty, be avoided. This disadvantage does not occur, however, when the central portion of the tube envelope, namely the portion which contains the delay line, is built up according to the invention with alternately assembled pole piece rings, nonmagnetic rings and soft magnetic homogenization rings.

Such an arrangement is represented in FIG. 6, in which reference numeral 5 designates the pole pieces of a permanent magnet system of the type illustrated in FIGS. 1 and 2. In contrast to the construction of FIGS. 1 and 2, however, the tube 7 is not fixedly inserted in the bores '6 of the pole pieces 5, but forms a part of the vacuum shell of a tube 14. There, advantageously, the individual rings can simultaneously be structural parts of the delay line of the tube, which is located in the tube spatially between the input coupling and the output coupling comprising hollow conductors 16 and 17. Reference numeral 14 designates the portion of the tube containing the electron gun and 15 the collector of the tube. The permanent magnet system is to be of hinged design capable of being swung open, making is possible to change the tube 14, whose electron gun 14' and collector 15 are thicker than the central portion of the tube, disposed in the magnetic system.

The invention is not limited to the examples of construction presented. In particular, it is not necessary that the tube 7 have the same length as the magnet system. Also, the tube can be subdivided into several component members. The length of the tube or of the parts, however, should in no case be less than three times the internal diameter of the tube 7.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

I claim:

1. A permanent magnet system for the bundled guidance of an electron beam over a relatively long distance, especially for traveling wave tubes, comprising permanent magnets arranged axially symmetrically to the electron path and pole pieces, which are arranged successively in electron beam direction and are traversed by the electron beam, magnetically connecting oppositely disposed like poles of the permanent magnets whereby there arises along the electron path a magnetic field alternating in direction, with approximately sine-shaped course of the magnetic field strength, the electron path being at least partially enclosed by a tube comprising alternately disposed soft magnetic and non-magnetic rings, the soft magnetic rings of an odd ordinal number bordering directly on the pole pieces and are symmetrically surrounded thereby, while the soft magnetic rings of an even ordinal number are, in each case, centered between adjacent pole pieces, as viewed in electron beam direction.

2. A permanent magnet system according to claim 1, the soft magnetic rings of an odd ordinal number having a greater axial length than the soft magnetic rings of an even ordinal number.

3. A permanent magnet system according to claim 2, wherein the non-magnetic rings have dimensions of the same order of magnitude as the soft magnetic rings of an even ordinal number.

4. A permanent magnet system according to claim 1, wherein each of the pole pieces which serve for the magnetic connection of like poles of the permanent magnets disposed opposite one another have a bore, into which the tube is disposed.

5. A permanent magnet system according to claim 4, wherein the pole piece rings, as viewed in electron beam direction, are wider than the portions of the pole pieces having said bores therein.

6. A permanent magnet system according to claim 5, wherein said tube forms the vacuum envelope of a traveling wave tube.

7. A permanent magnet system according to claim 6, wherein the permanent magnets and the pole pieces are so grouped about the electron path that the magnetic system, excluding the tube, is capable of being hinged for opening in two halves along a plane of symmetry running through the system axis.

8. A permanent magnet system according to claim 7, wherein the permanent magnets form a quadrangle extending in planes perpendicular to the electron beam and the pole pieces alternately diagonally connect oppositely disposed corners of the quadrangle.

9. A permanent magnet system according to claim 5, wherein the permanent magnets are constructed as annular magnets, which are arranged in succession and with like poles disposed adjacent one another, between which are positioned annular disk-shaped pole pieces.

10. A permanent magnet system according to claim 9, wherein the annular disk-shaped pole pieces have, in the vicinity of the electron path, extensions, with each pole piece and extensions comprising the pole piece rings, in which system the permanent magnets are constructed in the form of half-shells disposed between the annular disks extending radially outwardly from the tube.

References Cited UNITED STATES PATENTS 2,956,193 10/1960 De Wit 31384 BERNARD A. GILHEANY, Primary Examiner.

G. HARRIS, Assistant Examiner. 

1. A PERMANENT MAGNET SYSTEM FOR THE BUNDLED GUIDANCE OF AN ELECTRON BEAM OVER A RELATIVELY LONG DISTANCE, ESPECIALLY FOR TRAVELING WAVE TUBES, COMPRISING PERMANENT MAGNETS ARRANGED AXIALLY SYMMETRICALLY TO THE ELECTRON PATH AND POLE PIECES, WHICH ARE ARRANGED SUCCESSIVELY IN ELECTRON BEAM DIRECTION AND ARE TRAVERSED BY THE ELECTRON BEAM, MAGNETICALLY CONNECTING OPPOSITELY DISPOSED LIKE POLES OF THE PERMANENT MAGNETS WHEREBY THERE ARISES ALONG THE ELECTRON PATH A MAGNETIC FIELD ALTERNATING IN DIRECTION, WITH APPROXIMATELY SINE-SHAPED COURSE OF THE 